My second trimester ultrasound only showed up one kidney. Appointment was long, had to empty my bladder twice. What is the likelihood finding kidney?

One kidney in baby? The 2nd trim. Sono doesn't usually look at maternal structures, so i assume you are talking about the baby having only one kidney.You need a referral to a maternal-fetal medicine specialist for a level 2 sono; it would be unusual for a good sonographer to miss a kidney if it were there. Ur baby may have only one kidney, which shouldn't indicate genetic disorders and baby should likely b o/w health.
Test kidney function. Various possibilities- one, if born with kidney and kidneys functions gave been normal, just need to monitor bp, urine protein and functions from time to marine. Other possibility is that the kidney not seen on this imaging and may need another ultrasound or ct at a later date after delivering baby. Talk to your doctor and may need to see a nephrologist.